This invention relates to a magnetic disk device, especially to a magnetic disk device which is capable of storing control parameters specific to the magnetic disk device into a nonvolatile memory, and to a head suspension assembly for use in the magnetic disk device.
Generally, a magnetic disk device operates with plural magnetic disks, each having a magnetic layer which records data and is formed on a non-magnetic substrate, and the plural magnetic disks are stacked on a rotating shaft of a spindle motor. The magnetic disk device has magnetic heads for recording and reproducing data, which magnetic heads are each mounted on one end of a respective suspension, the other end of which is fixed to an end of an arm so as to be positioned on a respective one of the magnetic disk surfaces. The arm is driven by an actuator in response to a positioning signal. In a hard disk device having the above structure, the magnetic head is arranged so as to access a desired position while floating at a height of tens of manometers above the fast rotating magnetic disk surface during the recording and reproduction of data.
Data is recorded or reproduced to or from a track in the form of concentric circles on the magnetic disk by the magnetic head. Generally, a sequence of operations of the magnetic disk device is controlled by an MPU (Micro Processing Unit) that executes control programs based on control parameters that are stored in a nonvolatile memory or have been transferred into RAM (Random Access Memory) from the nonvolatile memory.
The magnetic disk device has various management data as follows: the device operation mode designed for each customer, such as ON/OFF operation of a cache and the setting of a master/slave status, parameters to be set up for each magnetic head, such as an optimum recording current and an optimum bias current obtained from recording and reproducing characteristics of each magnetic head, a physical offset position of a recording head and a reproducing head (hereafter referred to as the offset position), the amplifying gain of a head amplifier, and parameters to be set up for each magnetic head or data zone, such as filter constants. This management data will vary in every drive, and rewriting is required for a change of the set-up. Therefore, this data is generally stored in a semiconductor memory that operates as a nonvolatile rewritable memory, such as an EEPROM (Electrically Erasable and Programmable Read Only Memory) or a FROM (Flash Read Only Memory), or it may be stored in a management data area provided on a part of the magnetic disk.
According to recent trends toward downsizing and increasing the storage capacity of a magnetic disk device, a high performance magnetic head is required. As the high performance magnetic head, a composite type magnetic head comprising an individual reproducing head and a recording head is used. In this type of head, a MR (Magnetoresistive) head or a GMR (Giant Magnetoresistive) head is used for the reproducing head, and an inductive head formed by thin film technology is used for the recording head.
This type of head has complex structures, fluctuations in quality through the manufacturing process are larger, and recording and reproducing characteristics considerably vary in every magnetic head. To enable stable recording and reproducing at the desired recording density, only magnetic heads having a good characteristic must be assembled. For this purpose, before the magnetic head is assembled in the magnetic disk device, generally the recording and reproducing characteristics of a magnetic head in the form of a head suspension assembly (an assembly structure including suspensions which are provided for each recording and reproducing head, and an arm) are measured, and good magnetic heads are selected.
Items to be measured are resistance of the MR head, the physical positions (offset value) of the reproducing head and the recording head, the reproducing output voltage, the reproducing resolution, the over write characteristic, and the noise characteristic. At the time of measurement, the recording current of the recording head and bias current of the reproducing head are varied individually, and an optimum recording current and an optimum bias current are obtained.
In addition to an increase in the data transfer rate of the magnetic disk device, deterioration of the output signal is prevented by cutting down the length of a signal transmission line by mounting a head amplifier, which amplifies the reproducing signal from the magnetic head and drives the recording head, on the suspension or the arm (called a chip-on-suspension or chip-on-arm type). In this case, during the selecting measurement of the head mounted on the suspension assembly, the performance is evaluated with an output signal of the head amplifier, which shows integrated characteristics of the magnetic head characteristics and the head amplifier characteristics.
As described above, at the time of selecting measurement of the head mounted on suspension assembly, the optimization of the control parameters is executed by the following measurements: the measurement of the optimum recording current of the recording head, the measurement of the optimum bias current of the reproducing head, the measurement of the offset position of the recording head and the reproducing head, and the measurement of the head amplifier gain; and, the acceptance or rejection of each magnetic head is determined by setting up the optimum controlling parameter for each magnetic head. But these optimized control parameters are not memorized, and, at the time of shipping inspection of the magnetic disk device, a similar optimization procedure is executed again.
At the time of shipping inspection of the magnetic disk device, since the optimum recording current and the optimum bias current of each magnetic head are not known, a default value sufficient for starting the magnetic disk device is set up. The value to be set up is obtained from sampling the characteristics of plural magnetic disk devices, and it is a value designed to secure characteristic which will not to disturb operation of the magnetic disk drives during the shipping inspection; therefore, the default value will not correspond to the variation of the characteristics of each magnetic head, and it may happen that some of the magnetic disk drives are rejected at the time of shipping inspection of the magnetic disk devices for this reason. For example, at the time of shipping inspection of the recording and reproducing characteristic under the condition that the bias current of the reproducing head is set to a default value rather than to the optimum value for each head, it is possible that, if the default value is close to the upper or lower allowable limit of the inspected magnetic head, the inspected magnetic disk device will be rejected at the time of shipping inspection for failing to meet the required recording and reproducing characteristics. Therefore, there has been a problem that the yield is poor in the production of the devices.
Further, if the head suspension assembly is that of the chip-on-suspension type or chip-on-arm type, there is a drawback in that the signal level amplified by the head amplifier is merely evaluated at the time of selection measurement of the magnetic head of the head suspension assembly, and the signal level at the output terminals of the magnetic head cannot be measured accurately, since as the output signal is determined by the integrated characteristics of both the magnetic head and the head amplifier.
The present invention mainly uses the following structures:
A head suspension assembly which comprises an arm supported so as to rotate, an elastically flexible suspension having one end thereof fixed to an end of said arm and a magnetic head mounted on the other end thereof, and a signal transmission line which is fixed on said suspension and said arm and connects said magnetic head to a main FPC, wherein a nonvolatile memory which stores the control parameters of said magnetic head is mounted on the arm and said nonvolatile memory is electrically connected to said signal transmission line.
A head suspension assembly, which comprises an arm supported so as to rotate, an elastically flexible suspension having one end thereof fixed to an end of said arm and a magnetic head mounted on the other end thereof, and a signal transmission line which is fixed on said suspension and said arm and connects said magnetic head to a main FPC, wherein a head amplifier which transmits and receives signals to and from said magnetic head and a nonvolatile memory which stores the control parameter of said magnetic head and said head amplifier are mounted together on the arm, and said head amplifier and said nonvolatile memory are electrically connected to said signal transmission line.
A magnetic disk device, which comprises a magnetic disk, a read write circuit, a head suspension assembly which has a magnetic head, an arm supported so as to rotate, an elastically flexible suspension having one end thereof fixed to an end of said arm and a magnetic head mounted on the other end thereof, and a signal transmission line fixed on said suspension and said arm which connects said magnetic head to a main FPC, a storing means which stores control parameters specific to the magnetic disk device and the control parameters corresponding to an operating mode of the magnetic disk device, and control means which inspects or controls the magnetic disk device based on control programs and said control parameters stored in said storing means. Wherein, a nonvolatile memory, which stores optimized control parameters of the magnetic head obtained at the inspection of said head suspension assembly, is mounted on said head suspension assembly, and, at the time of inspection of the magnetic disk device, said control means operates to read out the default control parameters stored in said storing means together with the optimized control parameters stored in said nonvolatile memory for use in carrying out the inspection.